Seen it happen : When using GPU the GPU becames the bottleneck, when not using GPU the CPU becames the bottleneck.So when editing multiple panoramas please ask me each time press edit to open the panorama whether I want the panorama to use the GPU or not to use the GPU.

Of course, this should only be asked when user selected the new option in the global settings -> GPU processing called "Ask" that becames an alternative to the Enable option.

In case multiple GPU's are onboard one could be asked which GPU should be used